The semiconductor field has undergone tremendous change in the past fiew years largely due to the development of new devices with higher frequencies, greater stabilities, smaller sizes and greater bandwidths. Many of these developments have been due to the fact that new materials have been developed and new methods for processing these materials have been used. Some of the new techniques in fabricating semiconductor devices involve the use of smaller sizes, greater precision in locating various features on the semiconductor device, greater adherence of metallic substances to semiconductor surfaces and greater control in plating metals on semiconductor surfaces.
A particular example is a device involving one or more compound semiconductors. Various types of devices can be made using compound semiconductors including semiconductor lasers, photodetectors, light emitting diodes, and amplifiers. It is often necessary in the fabrication of such devices to particularly locate metallic substances to be used as conductors in precise places in the semiconductor device. A typical example is associated with the fabrication and structure of certain microwave semiconductor devices made from various compound semiconductors. Here, minimization of parasitic inductances is critical to good device performance. It permits higher frequency operation and more gain and bandwidth at these high frequencies. Also, more positive attachment of the metal such as silver to the metal pads insures good electrical contact and good thermal contact. This permits higher power handling capacity for the device and a higher and more predictable frequency characteristic for the device. Particularly advantageous is the use of silver in such applications because of its high chemical stability and its exceptionally high thermal and electrical conductivity characteristics. This permits high power handling capacity because of the large amount of heat conducted away from the semiconductor by the silver.
Particularly desirable is a reliable procedure for inducing chemical reduction at preselected areas in the compound semiconductor structure. In semiconductor processing, it is highly desirable that this be accomplished without electrical connection to individual devices. In most device fabrication procedures, a large number of devices are made from one semiconductor wafer and electrical connection to individual chips would be extremely difficult and time consuming. In particular, a silver plating procedure which was highly specific regarding where plating took place would be highly advantageous in fabricating many semiconductor devices.